Lithium primary and secondary cells having electrolytes formed of solvates of the tetrachloroaluminates of alkali and alkaline earth metals dissolved in sulfur dioxide are well known in the electrochemical power source art. Typical examples of variations of such cells are described in the following prior art teachings:
A known battery of this type is shown in the U.S. Pat. No. 4,513,067 to Kuo et al issued Apr. 23, 1985. This patent covers a battery with an alkali or alkaline earth anode, a carbon cathode, and a sulfur dioxide electrolyte. A basic battery including lithium tetrachloroaluminate dissolved in sulfur dioxide is described in Example No. 1 of this Kuo patent.
The Kuo patent is concerned with the construction of a battery wherein the cathode is made of porous carbon that may have an admixture therein, the admixture being a solid cathode active material that is substantially insoluble in the sulfur dioxide electrolyte and wherein the electrolyte salt used interacts with the sulfur dioxide solvent to minimize the reaction of the sulfur dioxide with the anode whereby to inhibit the formation of anode metal dithionite at the cathode surface.
Another U.S. Pat. No. 4,482,616 to Connolly et al issued on Nov. 13, 1984 is another example of a disclosure of a battery of this general type wherein the solubility of a lithium salt in the sulfur dioxide solvent system is said to be enhanced by the addition of a salt which contains a cation selected from the group of metal cation complexes consisting of ammonium cations and phosponium cations.
A discussion of an electrolyte including lithium tetrachloroaluminate and sulfur dioxide in combination with other alkali and alkaline earth tetrachloroaluminates in such batteries was published at the fall meeting of the Electrochemical Society in 1986 and was reported in Abstract #13 page 19 of the transactions covering that assembly.
A review of this prior art shows that while alkali and alkaline earth tetrachloroaluminates have been described as having been combined in different combinations to be dissolved in sulfur dioxide to form electrolytes in either primary or secondary batteries, no practical electrolyte has been suggested that includes a calcium tetrachloroaluminate used in combination with lithium tetrachloroaluminate dissolved in sulphur dioxide. In particular, the study covered in said Abstract #13 makes of record the fact that the "corrosion rate of lithium in the electrolyte containing Ca(AlCl.sub.4).sub.2 was found to be high", see Abstract #13 page 19 col. 2, lines 41-43.
Also in FIG. 6, that is referred to in the Abstract, the data showed that a very rapid rate of lithium corrosion in the first 14 days of storage with the Ca(AlCl.sub.4).sub.2 at 71.degree. C. occurred, as compared with various other electrolyte solutions in sulfur dioxide. Thus the art teaches away from the use of any amount of calcium tetrachloroaluminate in the electrolyte in a lithium/carbon type of battery.
There is no discussion in the Abstract #13 concerning the reason for the corrosion problem, the observation being made, only of the existence of the actual corrosion having taken place. The Abstract is devoid of any mention of a possible cause nor does it suggest a cure for this particular corrosion problem.